Electric discharge device and method of operating same



May 14, 1935. L. J. BUTTOLPH ELECTRIC DISCHARGE DEVICE AND METHOD OF OPERATING SAME Filed May 12, 1933 INVENTOR- Patented May 14, 1935 UNITED STATES PATENT OFFICE ELECTRIC DISCHARGE DEVICE AND METHOD OF OPERATING SAME Application May 12, 1933, Serial No. 670,772

4 Claims.

The present invention relates to electric gaseous discharge devices, and to a novel method and means for starting and operating the same.

The invention consists in a novel combination 5 of elements, and in a novel sequence of steps, as

hereinafter set forth and claimed.

A particular object of the invention is to provide a novel discharge device of the liquid cathode type which may be operated in either of two positions with the same operating characteristics. Another object of the invention is to provide means for operating an electric gaseous discharge lamp of the rectifying type with a minimum of auxiliary apparatus. A further object of my 2.3 invention is to provide a novel discharge device which is especially-adapted for use in combination with this novel operating means. Still another object of my invention is to provide a novel means for starting a discharge in a mercury vapor arc of the so-called high pressure type. Another object of my invention is to provide a novel method of operating electric gaseous discharge devices of the rectifying type. Still other objects and advantages of my novel invention will 25 appear from the following detailed specification or from an inspection of the accompanying drawing.

It is frequently desirable to operate the high pressure type mercury vapor arc lamps, such as are in extensive use for therapeutic purposes, with the arc tube in either a horizontal or a vertical position, in order to better direct the light therefrom for particular purposes. As heretofore constructed, however, these devices have ordinarily been limited by their structure to operation in but a single position, due to the fact that the flow of the liquid cathode incident to any change in position very materially alters the length of the arc path and thus radically changes the operating characteristics of the device. I have nowdiscovered that this difiiculty may be overcome by using a mercury vapor arc lamp having an extremely simple structure of my invention. This novel lamp has a tubular cathode chamber whose axis is at an angle of approximately 45 with that of the main arc tube, and hence rotation of the main arc tube through the desired 90 angle merely moves said cathode chamber between two symmetrical positions at 45 to the vertical, the length of the are being virtually the same in eitherposition, or at any position therebetween.

The amount of auxiliary apparatus which has heretofore been employed in operating mercury arc lamps, as well as other types of lamps having similar rectifying characteristics, such as those operating with a thermionic cathode, on alternating current has also been a disadvantage, due both to the high initial cost, and to the bulkiness and weight of this apparatus. I have now dis- 5 covered that virtually all of this auxiliary apparatus, including the usual autotransformer, can

be eliminated by utilizing a novel connection for the lamp, and by operating the lamp in a novel manner. According to my invention the two 10 anodes usually provided in a lamp intended for use with alternating current are connected directly to opposite sides of an alternating current line, and one side of said line is likewise connected to the cathode through an inductance. With this arrangement the inductance not only performs the usual function of stabilizing the are, but also stores energy during one half cycle and gives it up during the next half cycle, whereby full wave operation is obtained without the use of a transformer.

Heretofore these high pressure mercury vapor arcs have always been started by the cumbersome method of tilting the lamp until the mercury momentarily bridges the electrodes, the are at separation establishing the desired are between the electrodes. Even this method of starting is unsatisfactory, for when the vapor pressure within the lamp is so high that the discharge has the characteristic stringy appearance of a socalled high pressure are it is impossible to restart the arc by this method, in case of momentary failure, until the lamp has cooled for at least five minutes. I have now discovered that by using a novel type of shifter or switch I can start an are virtually instantaneously in my novel lamp, whether hot or cold, by means of a high voltage surge, although heretofore exhaustive test has. demonstrated that this surge starting method could not be successfully used in lamps of this type. The novel shifter which is thus an essential feature of my novel structure is a switch having solid metallic contacts which operate within an extremely high vacuum, such as disclosed by Warren R. Walker in his Patent 1,984,505, granted December 18, 1934. I have discovered that this type of switch, unlike those previously used, can be made to produce a voltage surge in the inductance of suflicient potential to restart an are even when the pressure is so high that it can not be started by the tilting method previously referred to. Furthermore mercury arc lamps having insufiicient mercury therein to bridge the electrodes may now likewise be started in this novel man- 'ner, regardless of whether they are of the mercury electrode or of the thermionic electrode type. Likewise this novel method of starting is effective with these mercury are devices, whether they be operated on direct current, or with a simple or rectified discharge on' alternating current.

For the purpose of illustrating 'my invention I have shown a preferred embodiment thereof in the accompanying drawing, in which I Fig. 1 is an elevational view of my novel lamp, together with a schematic diagram of my novel.

' operating circuit therefor,'the lamp being shown with the arc tube horizontal, and

Fig. 2 is a similar view, showing the lamp in its vertical operating position.

As shown in the drawing my novel mercury vapor arc lamp has an arc tube I of fused silica or the like into one end of which open two parallel anode chambers 2 and 2 which are substantially tubular in form" and which lie close to each other. A pair of inleads 3 and 3 of tungsten or the like are sealed into the ends of the respective anode chambers through a conventional graded joint, each of said inleads'supporting on the end the like which is sealed into the end of the chamber 5 through a conventional graded seal makes contact with the mercury cathode I which extends to a point slightly below the level of'the arc tube I when the lamp is in the position shown in Fig. 1. is virtually the same distance from the anodes 4 and 4' when the lamp is in either of the positions shown in Figs. 1 and 2, or in any position therebetween. A metal sleeve 8 is clamped about the cathode chamber 5 with one edge thereof adjacent to the surface of the mercury I. v

The anode inleads 3 and 3' are connected to opposite terminals of any suitable source of alternating current, of say H0 volts potential. An inductance 9 is connected between the cathode inlead 6 and one. of said terminals, preferably the same terminal which is connected to the anode inlead 3'. This inductance is preferably relatively large, as compared to the usual stabilizing inductances, so that it can absorb considerable energy. For example, in the case of a lamp operatirig' on volts with a root mean square current of 5.5 amperes I preferably use an inductance of the order of V; henry. The sleeve 8 is connected to the other terminal of said line, while a switch III which is normally closed but which is adapted to be magnetically opened by the inductance 9, is connected between said inductance and the same terminal as the sleeve 8. Said switch I0 is preferably ahighly evacuated switch with solid metal contacts, and is schematically shown in the form ofthe switch disclosed by Warren H. Walker in his Patent 1,984,505, granted December 18, 1934, which has proved extremely effective in this n'ovel circuit.

.In this switch the fixed contacts are bridged by a freely movable, magnetically operated bar H.

In the use and operation of this novel appara-' tus, as soon as an alternating current potential is applied thereto current fiows through the in- With this construction the cathode l ductance 9 and the switch The magnetic field thus produced about the inductance 9 causes the switch J0 to be opened, whereupon the collapsing magnetic field produces an extremely high voltage surge of at least several thousand volts which is impressed upon the cathode I. If the polarity of the source is such that the anode 4 is negative at the instant the switch l0 opens the circuit this surge is not effective to start the discharge. Hence the switch I is allowed to reclose as soon as the inductance 9 is deenergized, thus again energizing said inductance and reopening switch III as before. If now the polarity of the source is such that the anode 4 is positive at-the instant said switch I ll opens the ensuing voltage surge makes the cathode intensely negative with respect to, both of the anodes 4 and 4', and to the sleeve 8. A disruptive discharge thereupon occurs at said cathode, establishing a hot spot on the mercury surface and ionizing the gaseous atmosphere within the arc tube. If the anode 4 is still positive with respect to the cathode 1 at this in-, stant the main discharge is initiated therefrom, and the current thus flowing again energizes the inductance 9, and thus causes the switch III to be maintained in an open circuit position. At the end of the half cycle the anode 4 becomes negative, so that current canno longer flow therefrom to the cathode I. The anode 4 is connected to the same side of the line as the cathode I, and hence it is obvious that the line potential is ineffective to maintain a discharge from said anode 4'. As the discharge current from the anode 4 begins to fall to zero, however, the magnetic field about the inductance 9 begins to collapse, inducing a potential in said inductance which makes the anode 4' sufficiently positive with respect to the cathode 1 to produce a current fiow of almost the same value as was flowing from the anode 4. This current slightly decreases during this half cycle, but due to the large energy storage in the inductance 9 this decrease is not enough to markedly afi'ect the light emission from the tube, so that there is no observable flicker therein, as there would be if this were a mere keep-alive circuit. As the anode 4 again becomes positive the discharge shifts thereto and the magnetic energy stored in the inductance 9 is again increased, this cycle being continued so long as the energy is applied. The discharge is thus operated as a full-wave rectified discharge, despite the fact that energy is only drawn from the line on alternate half cycles. The use of this novel circuit is, of course, not limited to mercury vapor lamps, for equal advantages are obtained-when it is used with any other type of lamp, such as those with thermionic cathodes, which have similar rectifying characteristics.

Heretofore it has been impossible to restart mercury vapor arc lamps of any type in which the vapor pressure is so high that the discharge is markedly constricted or stringy, as distinguished from the difiuse discharge at low pressures, without avery considerable delay period of at least five minutes, during which the lamp cooled and the vapor pressure thus decreased. This has been a considerable source of annoyance, for if even a momentary line failure chanced to occur during treatment of a patient, the irradiation was not only stopped, but could not be restarted for a considerable period, of the order of at least five minutes. With my novel apparatus this difliculty has been overcome, for virtually instantaneous starting is now attainable at all times, irrespective of whether the lamp is at room temperature. This the mercury shifters previously used, can interrupt the inductive circuit while the current is still very large. Thus approximately all the energy stored in the inductance is available to produce the voltage surge, which now for the first time is of sumcient value to immediately restart the arc in a high pressure quartz lamp while it is still hot. As a, result I now find it possible to immediately restart a high-pressure mercury arc at a time when it could not be restarted by any of the methods heretofore available. As a result I am now able to produce for the first time an automatic,'sel1 -starting continuously operating mercury arc irrespective. of the vapor pressure attained therein during operation, thus doing away with starting by hand tilting and avoiding the live minutes wait to restart consequent upon the interruption of operatlon'oi. such lamps, as heretofore made and sold.

While I haveillustrated by invention my reference to a particular embodiment thereof it is to be understood that it is not limited thereto, but that various changes. omissions, or substitutions,

within the scope oi the appended claims may be.

I the paths from said cathode to said anodes being of unequal length. means to connect a source of alternating current between said anodes, and a a connection an inductance between said cathode and the anode which is nearer said cathode.

2. In combination, an electric gaseous discharge lamp .oi' the rectifying type having an elongated arc tube, a cathode at one end thereof, and a pair of anodes at theopposite end 01' saidarc tube, the paths from said cathode to said anodes being of unequal length, means to connect a source of alternating current between said anodes, and a connection including an inductance between said cathode and the anode which is nearer said cathode, said inductance being. sumciently large to riected to said cathode, means to energize saidinductance independently of current flow through said inductance, said last mentioned means including a vacuum switch having electrodes of solid metal, and a sleeve about said lamp adjacent to said cathode, said sleeve being connected to the terminal of said switch which is remote from" mam; .1. summit. 

